The harmful effects of solar radiation can have a huge negative impact on humans. Commercial sunscreens contain “filters” that, in the organic filters case, absorb ultraviolet light. When a molecule absorbs light, the absorbed photon can excite an electron from a low energy (bonding) orbital to a higher energy orbital (non-bonding). The “excited” electron has to release energy to return to the ground state. There are several pathways for this electron to release energy to return to its ground state: fluorescence, thermal, and chemical reactions to list a few. It is important in cosmetic sunscreens that the organic filters (i.e. the molecules that absorb UV at specified wavelengths) are returned to their ground state as quickly as possible and without chemical modification. One of the more efficient ways to achieve this in a commercial product is to include “Photo-stabilizers” that can “absorb” the energy of the excited electrons.
U.S. Pat. No. 9,145,383 to Bonda teaches conjugated fused polycyclic molecules that quench, dissipate, and/or otherwise resolve excited state energy, normally by way of releasing it as heat. The current invention uses a similar mechanism as described by Bonda, but has the added benefit of being a polymeric material capable of forming a very water-resistant film.
Esters of salicylic acid have been used as sunscreens and also have been prepared and used primarily as defoliating agents for the skin and conditioning agents for hair. Esters synthesized from longer chain di-acids, such as azelic, adipic, or maleic acid tend to yield esters with good low temperature characteristics. The esters of this type seem to have a “heavy” aesthetic. The esterification of these di-acids with a low molecular weight branched alcohols have produced esters with less “heavy” sticky aesthetic.
Esters of dimer acids or dimer alcohol are primarily known for their anti-irritating characteristics when employed in a formulation, however the aesthetics of these esters are much heavier than desired in most formulation.
Esters derived from benzoic acid, have been prepared and been used as sunscreen synergists as well as defoliants for the skin. The properties of these esters arise from the aromatic nature of the benzoic acid starting material. The esterification of benzoic acid does not affect the aromatic nature of the starting material or monomer, thus making esters and polymeric species of these materials attractive in the cosmetic industry.
All of the esters above have been used in the cosmetic industry to maximize performance in a formulation. Surprising and unexpectedly, we have found that the specific polyesters of the present invention, possesses the highly desirable cosmetic properties including but not limited to skin feel, film formation and conditioning benefits.
An additional aspect of the present invention comes from the presence of aromatic groups in these polyesters. The aromatic groups allow for significant improvement of the sun protection factor, while in and of themselves not being sunscreen actives. Put another way, all aromatic compounds have a wavelength in which they absorb ultraviolet radiation. However, only some classified as sunscreen actives absorb in either the UVA or UVB wavelengths. It is compounds that absorb in the non-UVA, UVB that are useful in the present invention.